ADS can now return map of top level items.

The map shows the name & workspace of any items that are groups or
not members of groups.
Refs #7708
Implemented Workspace::toString for all workspace types.

This now returns a human-readable string detailing the structure
of the workspace.
Refs #7708
First cut at putting back lazy-population of the MantidDock

Still needs icons & WorkspaceGroup sub items.
Refs #7708
Modified MantidDockWidget to use Workspace::toString

This will ease future extensions should the ADS ever be made to handle more
than workspaces.
Refs #7708
Only sort in MantidDock when tree is not updating.

Refs #7708
Removed unused code in MantidDock.

Refs #7708
Remove obselete InfoNode class & all references.

Refs #7708
Attach DataItem::toString to Python __repr__ method.

Refs #7708
Merge branch 'bugfix/7708_lazy_dock_workspace_details' into develop